1. Field of the Invention
The present invention relates to a radio frequency identification tag (RFID tag) that exchanges information with external devices in a non-contact manner, and to a method of manufacturing the RFID tag.
2. Description of the Related Art
Recently, there have been proposed various types of RFID tag that exchange information with external devices typified by reader-writers in a non-contact manner by radio wave (see for example, Japanese Patent Application Publication Nos. 2000-311226, 2000-200332, and 2001-351082). As one type of RFID tag, there is proposed a RFID tag having such a structure that an antenna pattern for wireless communications and a circuit chip are mounted on a base sheet made of plastics, paper or the like. It has been conceived to use this type of RFID tag in such a way that the RFID tag is affixed to an article or the like to exchange information about the article with an external device so that the article can be identified.
FIG. 1 shows a schematic sectional view of an internal component (inlay) that is an element of an example of a RFID tag.
An inlay 10 shown in FIG. 1 used for a RFID tag has such a structure that an antenna 12 formed by a conductor pattern is laid on a flexible sheet-like base 13 made of a PET film or the like and a circuit chip 13 is disposed on the antenna 12. In this circuit chip 13, a circuit for exchanging information with an external device via the antenna 12 is built in. The circuit chip 13 has connection terminals 13a formed on the underside of the circuit chip 13, which are soldered and electrically connected to the antenna 12. The circuit chip 13 is fixed on the base 11 by an adhesive 14 surrounding the circuit chip 13. The RFID tag has such a structure that the inlay 10 shown as an example in FIG. 1 is enclosed in the RFID tag.
FIGS. 2(A) and 2(B) are diagrams respectively showing a plan view and a sectional view of a RFID tag 20A.
FIG. 2(B) illustrates a section X-X of the RFID tag 20A shown in FIG. 2(A).
The RFID tag 20A has such a structure that the inlay 10 described above with reference to FIG. 1 is interposed between two sealants 21 and 22, and these sealants 21 and 22 are fused together by heat and pressure thereby enclosing the inlay 10. As a material of the sealants 21 and 22, for example, thermoplastic urethane, PET or the like can be used.
Incidentally, for the purpose of aiding the understanding of these sealants 21 and 22, a line is drawn between the two sealants 21 and 22 in FIG. 2(B) to show them as if they are separated. Actually however, the sealants 21 and 22 are fused with each other to be one piece.
Here, a tabular structure, which is formed by the inlay 10 enclosed by the two sealants 21 and 22, is referred to as a tag main body 200. On the entire top surface of the tag main body 200, a print layer 23 is formed by printing, and a protective film 24 for protecting the print layer 23 is disposed thereon.
Incidentally, Japanese Patent Application Publication No. 2001-351082 discloses a RFID tag having no protective film and thus a print surface is exposed, Japanese Patent Application Publication No. 2002-207984 discloses a structure in which an inlay for RFID tag is enclosed, and Japanese Patent Application Publication No. 2001-66990 discloses a structure in which an IC tag (inlay for RFID tag) is enclosed.
A RFID tag is provided with a print for the purpose of enhancing the design of the RFID tag, visually checking the information such as ID, and the like. If an RFID tag is provided with a print exposed at the surface of the RFID tag as disclosed in Japanese Patent Application Publication No. 2002-207984, a problem such as removal or bleaching of the print is very likely to occur when the RFID tag is used outdoors or undergoes environmental stresses such as cleaning.
Besides the printing, there is another technique known as laser marking that forms grooves in the surface of a RFID tag by means of laser to record information. However, the laser marking has such problems that what is formed by the laser marking is more difficult to see than that formed by the printing and the laser marking is incapable of providing color printing.
In order to solve these problems, it is conceivable to dispose the protective film 24 on the print layer 23 as described with reference to FIG. 2. However, water and the like are very likely to enter through the sides of the protective film 24 thereby peeling off the protective film 24.
Further, if the surface of the RFID tag after being molded is provided with a print and then coated with the protective film, it is expected that the number of manufacturing processes will increase, thereby increasing the cost.